The objective of these studies is to determine the pattern(s) of tissue injury resulting from the administration of antigen via the gastrointestinal tract to animals that have been immunized against the corresponding antigen. These studies may permit us to define an animal model of allergic gastroenteropathy involving the humoral phase of the immune response. Stages in the development of the model include: 1. The demonstration of uptake of intact proteins (and large fragments?) by the gastrointestinal tract of adult rats in vivo. 2. Exploration of the effects of physiologic or pathologic alterations of the host on the uptake of intact proteins or large fragments. 3. Study of the influence of an intestinal IgE antibody-mediated hypersensitivity reaction on the uptake of the specific antigen against which IgE antibodies are directed, as well as on the uptake of unrelated antigens. 4. Study of the disposition of antigen administered via the gastrointestinal tract to rats possessing both tissue-fixed (and possibly free) IgE, as well as circulating IgG antibodies. 5. Studies of the local and remote tissue injury resulting from the ingestion of protein antigens by rats possessing IgE and IgG antibodies directed against the ingested antigens.